1. Field of the Invention
The invention relates to a phased array antenna system for radar applications, including at least two phased array antenna faces suitable for producing RF transmitter pulses, each antenna face provided with an RF amplifier for producing RF pulses of an at least substantially constant amplitude, a supply network for providing the T/R modules with an RF input signal and a control unit for generating control signals for the individual T/R modules.
2. Discussion of the Background
Antenna systems of this type are known under the name of multiface phased array antenna system and are used, for instance, on board naval ships for a considerable number of tasks which until recently required the availability of a variety of fire-control and surveillance radar systems. Besides, these systems are of a sturdy construction which ensures their sustained operation also in the event of a failure of part of the T/R modules.
The common assumption with multiface phased array antenna systems is that the various faces are capable of operating independently. A more specific assumption is that transmission of RF pulses by one antenna face and reception by another face may coincide, or worded differently, that the isolation between the various faces is satisfactory. To this end, the phased array antenna system is designed on the basis of a predetermined isolation between adjacent antenna faces. This isolation is however only realized by stipulating a predetermined frequency difference for the transmissions of adjacent antenna faces. This frequency difference can be easily determined on the basis of the required isolation and maximum power, the bandwidth and the spectral purity of the RF transmitter pulses.
When employing active T/R modules, crosstalk from a transmitting face to a receiving face is still found to occur during a leading or trailing edge of an RF transmitter pulse. A solution well-known in the art to crosstalk problems of this type is by providing the RF transmitter pulse with a tapering. In the event of a given frequency difference between the transmitting face and the receiving face, the required degree of tapering can, with a view to attaining a specified isolation, be determined in a manner known in itself. For a phased array antenna, this knowledge is insufficient. An RF input signal, provided with a required tapering and subsequently applied to an active T/R module, is found to produce a practically untapered RF transmitter pulse. This is due to the fact that the RF amplifiers in the active T/R modules are driven into saturation in order to realize an acceptable level of efficiency. A good efficiency is required from an economic point of view, but also serves to reduce the load on the already complicated thermoregulation system incorporated in the phased array antenna system.